Extreme ultra violet (EUV) lithographic masks are used during the manufacturing process of semiconductor wafers and other modern electrical components. Defects of EUV lithographic masks are duplicated on multiple electrical components and thus are very costly. In order to protect EUV lithographic masks these masks are usually covered (or placed below) by pellicles.
EUV lithographic masks should be inspected in order to detect defects. The detection typically includes scanning the EUV lithographic masks with low energy electrons and detecting these low energy electrons.
It has been found that some modern pellicles prevent (or at least dramatically reduce) the passage of low energy electrons through the pellicles and thus prevent inspection of EUV lithographic masks that are protected by pellicles.
There is a growing need to inspect EUV lithographic masks that are protected by pellicles.